1. Field of the Invention
This invention relates to an electroluminescence(EL) device with excellent luminescence properties.
2. Description of the Related Art
An organic electroluminescence device is a self-light emitting device utilizing the principle that applying an electric field to a fluorescent substance causes its light emission through recombination energy of positive holes injected from an anode and electrons from a cathode. Since C. W. Tang et al reported an organic EL device of a layered type driven by a low voltage (C. W. Tang, S. A. VanSlyke, Applied Physics Letters, Vol.51, 913(1987)), an organic EL device composed of organic materials has been intensively investigated. Tang et al. has used tris(8-hydroxyquinoline) aluminum in a luminescent layer and a triphenyl diamine derivative in a hole-transporting layer. A layered structure has advantages such as an improved efficiency of injecting positive holes into a luminescent layer; an improved efficiency of generating excitons obtained from carrier recombination, by blocking electrons injected from a cathode; and confinement of excitons generated in a luminescent layer. As is shown above, well-known structures for an organic EL device include a two-layer type comprising a hole-transporting(injection) layer and an electron-transporting luminescent layer, and a three-layer type comprising a hole-transporting(injection) layer, a luminescent layer and an electron-transporting (injection) layer. In these layered structures of devices, various device structures and manufacturing processes have been devised for improving an efficiency of recombination of injected positive holes and electrons.
Conventionally known light emission materials are chelate complexes such as tris(8-hydroxyquinoline) aluminum complex, coumarin derivatives, tetraphenylbutadiene derivatives, bisstyryl arylenes and oxadiazole derivatives. It has been reported that they may give a luminescent color in the visible region from blue to red, and thus they are promising for realizing a color-display device(e.g., JP-A 8-239655, JP-A 7-138561 and JP-A 3-200889).
Electron-transporting materials are well-known e.g., oxadiazole derivatives and triazole derivatives.
Hole-transporting materials are well-known, e.g., triphenylamines and aromatic diamines such as 4,4xe2x80x2,4xe2x80x3-tris(3-methylphenylphenylamino)triphenylamine, which is a star-burst molecule, and N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(3-methylphenyl)-[1,1xe2x80x2-biphenyl]-4,4xe2x80x2-diamine (e.g., JP-A 8-20771, JP-A 8-40995, JP-A 8-40997, JP-A 8-53397, JP-A 8-87122). Recently, 3,3xe2x80x2-diamino-1,1xe2x80x2-binaphtyl derivatives have been disclosed in JP-A 9-255948. It has been described that the above compound has a higher glass-transition temperature, and thus, when used as a hole-transporting material, may give an organic EL device highly reliable under a drive condition of a high current density. There is, however, a problem of a low luminance.
There have been recently disclosed or reported organic EL devices with a high luminance and a long life, which are, however, not necessarily satisfactory. It has been, therefore, desired to develop materials exhibiting a high performance. Thus, an objective of this invention is to provide an organic EL device with an improved luminance.
We have intensely investigated for solving the above problems, and have obtained the following observations on an organic EL device prepared by using at least one of the compounds selected from the group consisting of;
(1) particular bianthryl compounds[I],
(2) particular binaphthyl compounds[II],
(3) particular trianthrylene compounds[III], and
(4 ) particular naphthylanthracene compounds[IV] as a luminescent material, leading to this invention.
1. An organic EL device prepared by using the particular bianthryl compound[I] can exhibit a higher-luminance luminescence than a conventional one. The material has a good carrier transport property. An organic EL device prepared by using the material as a hole- or electron-transporting material, or by using a mixture layer of the above material and another hole- or electron-transporting material, may exhibit a higher-luminance luminescence than a conventional one. An organic EL device may give a particularly high-luminance luminescence, when employing the above bianthryl compound substituted with a diarylamino group as a luminescent, hole-transporting or electron-transporting material. An organic EL device may give a particularly high-luminance luminescence, when employing the above bianthryl compound whose aryl group is substituted with a styryl group, as a luminescent, hole-transporting or electron-transporting material.
2. A luminance of an organic EL device may be improved by using the particular binaphthyl compound[II] in a hole-transporting layer. In addition, an organic EL is provided, in which the binaphthyl compound is used as a luminescent material and/or an electron-transporting material.
3. An organic EL device prepared by using the particular trianthrylene compound[III] can exhibit a higher-luminance luminescence than a conventional one. The material has a good carrier transport property. An organic EL device may exhibit a higher-luminance luminescence than a conventional one, by forming a hole- or electron-transporting layer made of the material or of a mixture of the material and another hole- or electron-transporting material.
An organic EL device may give a particularly high-luminance luminescence, when employing the above trianthrylene compound substituted with a diarylamino group as a luminescent, hole-transporting or electron-transporting material. An organic EL device may give a particularly high-luminance luminescence, when employing the above trianthrylene compound whose aryl group is substituted with a styryl group, as a luminescent, hole-transporting or electron-transporting material.
4. An organic EL device prepared by using the particular naphthylanthracene compound[IV] can exhibit a higher-luminance luminescence than a conventional one. The material has a good carrier transport property. An organic EL device may exhibit a higher-luminance luminescence than a conventional one, by forming a hole- or electron-transporting layer made of the material or of a mixture of the material and another hole- or electron-transporting material.
An organic EL device may give a particularly high-luminance luminescence, when employing the above naphthylanthracene compound substituted with a diarylamino group as a luminescent, hole-transporting or electron-transporting material. An organic EL device may give a particularly high-luminance luminescence, when employing the above naphthylanthracene compound whose aryl group is substituted with a styryl group, as a luminescent, hole-transporting or electron-transporting material.
An organic EL device according to this invention which employs a compound or compounds selected from the group consisting of the above four types of compounds, can exhibit a higher-luminance luminescence than a conventional one, indicating that this invention is highly effective.